This invention relates to a unit injector system for internal combustion engines, and more particularly to such a system for diesel engines having a pump element for subjecting fuel in a pump chamber to high pressure, an injection element for injecting the pressurized fuel into the combustion chamber of the engine, and a control valve which opens and closes a connection between the pump chamber and a low-pressure chamber.
One such unit injector system, or UIS for short, is described in German Patent Disclosure DE 198 35 494, which had not been published by the priority date of the present application. In a UIS, the pump element and the injection element form a unit, and one such unit is typically built into each cylinder head of the engine. The drive of the UIS is done either via a tappet or indirectly from the camshaft via rockers.
A 2/2-way valve can be used as the control valve. In the first position of the 2/2-way valve, the connection between the pump chamber and the low-pressure chamber is open. Then filling of the pump chamber is possible during the intake stroke, and during the pumping stroke a return flow of fuel to the low-pressure chamber is possible. In the second position of the 2/2-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. Then, the pressure required for injecting the fuel is built up in the pump chamber. Once the pressure exceeds a predetermined opening pressure, the injection element opens, and the pressurized fuel is injected into the engine combustion chamber. The closing time of the control valve thus determines the injection onset. The injection quantity depends on the closing duration of the control valve. To reduce fuel consumption and pollutants, a so-called preinjection of a slight fuel quantity can be performed before the actual main injection.
The object of the invention is to furnish a unit injector system of the type described at the outset, with preinjection, that is simple in structure and can be produced economically.
In a unit injector system for internal combustion engines, in particular diesel engines, having a pump element for subjecting fuel in a pump chamber to high pressure, having an injection element for injecting the pressurized fuel into the combustion chamber of the engine, and having a control valve, which opens and closes a connection between the pump chamber and a low-pressure chamber, this object is attained in that a throttle device is disposed in the connection between the pump chamber and the low-pressure chamber, and there is a flow through the throttle device as a function of the position of the control valve.
The throttle limits the fuel quantity that flows through the connection between the pump chamber and the low-pressure chamber and thus in a simple way makes it possible to define a preinjection.
One embodiment of the invention is characterized in that the control valve includes a first valve body with a first valve seat face and a second valve body with a second valve seat face, which are received, capable of reciprocation, in a housing. The cooperation of the two valve bodies enables a precise setting of different strokes of the valve bodies.
A further embodiment of the invention is characterized in that the control valve is a 3/3-way valve. In the first position of the 3/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the second position of the 3/3-way valve, because of the throttle device, less fuel flows through the connection between the pump chamber and the low-pressure chamber than in the third valve position. The lesser fuel quantity is used for the preinjection. In the third position of the 3/3-way valve, a connection, provided parallel to the throttle device, to the low-pressure chamber enables normal filling of the pump chamber.
A further embodiment of the invention is characterized in that in a first valve position, the first valve body is spaced apart from the second valve body, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face rest on their associated valve seat edges, as a result of which the connection between the pump chamber and a low-pressure chamber is closed;
that in a second valve position, the first valve body comes to rest on the second valve body, and the first valve body having the first valve seat face lifts from its associated valve seat edge, as a result of which fuel can flow to a throttle in the second valve body, which throttle communicates with the low-pressure chamber;
and that in a third valve position, the second valve body comes to rest on a stroke end stop, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face are lifted from their associated valve seat edges, as a result of which a connection without a throttle is opened up to the low-pressure chamber. The first valve body can be kept in contact, with the first valve seat face, on the associated valve seat edge by a first valve closing spring. The actuation of the first valve body can be done by means of a magnet or a piezoelectric actuator. The second valve body can be kept in contact, with the second valve seat face, on the associated valve seat edge by means of a second valve closing spring. As a result, it is assured that in the unactuated state, the control valve is closed.
A further embodiment of the invention is characterized in that a groove is recessed out of the end face, toward the second valve body, of the first valve body. The groove assures that fuel can reach the throttle in the second valve body when the two valve bodies are in contact with one another.
A further embodiment of the invention is characterized in that a groove is embodied on the stroke end stop. The groove prevents the formation of a pressure cushion during operation between the second valve body and the stroke end stop, that could unfavorably affect the injection performance.
A further embodiment of the invention is characterized in that the control valve is a 2/3-way valve. In the first position of the 2/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the first position of the 2/3-way valve, the connection between the pump chamber and the low-pressure chamber is interrupted. In the second position of the 2/3-way valve, because of the throttle device, less fuel flows through the connection between the pump chamber and the low-pressure chamber than in the third valve position. The lesser fuel quantity is used for the preinjection. In the third position of the 2/3-way valve, a connection, provided parallel to the throttle device, to the low-pressure chamber enables normal filling of the pump chamber.
A further embodiment of the invention is characterized in that the first valve body has a central bore, in which part of the second valve body is displaceably received;
that in a first valve position, the first valve body is spaced apart from a stroke stop on the second valve body, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face rest on their associated valve seat edges, as a result of which the connection between the pump chamber and the low-pressure chamber is closed;
that in a second valve position, the first valve body comes to rest on the stroke stop of the second valve body, and the first valve body having the first valve seat face lifts from its associated valve seat edge, as a result of which fuel can flow to a throttle in the second valve body, which throttle communicates with the low-pressure chamber;
and that in a third valve position, the second valve body comes to rest on a stroke end stop, and both the first valve body having the first valve seat face and the second valve body having the second valve seat face are lifted from their associated valve seat edges, as a result of which a connection to the low-pressure chamber without a throttle is opened up. The first valve body can be kept in contact, with the first valve seat face, on the associated valve seat edge by a first valve closing spring. The actuation of the first valve body can be done by means of a magnet or a piezoelectric actuator. The second valve body can be kept in contact, with the second valve seat face, on the associated valve seat edge by means of a second valve closing spring. As a result, it is assured that in the unactuated state, the control valve is closed.
A further embodiment of the invention is characterized in that the second valve body in the built-in state is substantially balanced in terms of force. As a result, it is attained that a closing spring of small dimensions can be used for the second valve body.
A further embodiment of the invention is characterized in that the throttle has a constant flow diameter. The throttle can be manufactured as an independent component with high precision. As a result, it is possible to achieve a preinjection quantity with highly accurate replicability.